Bulk properties of nonionic surfactant and chitosan mixtures

Bulk properties in mixtures of the nonionic surfactant Lutrol® F127 and cationic polyelectrolyte chitosan in water and acetate buffer (pH 6.0 and 6.5 and ionic strength 0.1 and 0.5, respectively) were studied by fluorescence spectroscopy, dynamic light scattering and zeta potential measurements. It was observed that the addition of chitosan to F127 systems in water had little effect on critical micelle concentration (cmc) values. On the contrary, the addition of chitosan to F127 systems in acetate buffer shifted cmc to higher values. Independently of pH and ionic strength, the cmc increase was more pronounced as the chitosan concentration in the system increased. The antagonistic mixing behaviour of the present nonionic surfactant and polyelectrolyte was observed at pH 6.5 and an ionic strength of 0.5 at 34 °C. The micelles in mixed F127/chitosan systems had an average hydrodynamic diameter of 25 nm and were larger than F127 micelles themselves (22.5 nm). The zeta potential of micelles in F127 water systems and in both acetate buffer systems was almost neutral, due to the nonionic nature of F127. In water and both acetate buffer mixed F127/chitosan systems, the zeta potential of micelles was positive and increased with increasing chitosan concentration, due to the electropositive charge of chitosan. The effect was more pronounced in water systems. Results are discussed in terms of electrostatic, hydrophobic and interpolymer interactions.